Hi there, Kevin.
Thank you for reaching out to us. Based on your photos, it appears you have either the Series 351 or Series 390 channel balances. The difference between these two similar-looking balances is the depth of the bottom fitting. The photo below will show you what I mean.
The "33" at the end of the balance stamp may represent the sash weight so if that's the case I recommend the 2765 option. A pair of balances with this stamp will support a sash weighing 33 to 36 pounds. You can always weigh the window sash on a scale to confirm.
Let me know if you have any questions!
My pleasure! Best of luck with the repair and please let me know if I can be of further help.
